This invention relates to apparatus for forming a hem in a moving web of film and more particularly to an improved hem folder tucker bar for use in making hems in the manufacture of draw tape plastic bags.
Bags made of thin polyethylene material have been used in various sizes. Smaller bags are used in the packaging of sandwiches and the like; larger bags are used as shopping bags; and even larger bags are used for containing trash.
A particularly advantageous closure for such a bag includes a draw tape constructed from the same polyethylene material. U.S. Pat. No. 3,029,853--Piazzi, and British Pat. No. 1,125,363--Jortikka are examples of draw tape bags. Such closures have been successfully employed on these bags.
Draw tape closures for large trash bags, and the manufacture of these draw tape trash bags, are described in the related applications identified below.
Forming the hem, into which the tape is inserted, is shown, for example, in U.S. Pats. Nos. 2,897,729--Ashton et al, 3,058,402--Krugler, 3,058,403--Krugler and in pending applications of applicant's assignee including "Method and Apparatus for Forming Hems in Superposed Pliable Panels", Boyd et al, Ser. No. 652,255, filed Sept. 20, 1984 now U.S. Pat. No. 4,717,008 and "HEM FOLDER WITH INTEGRAL TAPE INSERTER FOR MAKING DRAW TAPE BAGS," Herrington, Ser. No. 871,238 filed June 6, 1986, now U.S. Pat. No. 4714455. Apparatus for sealing a hem in a moving web of film is disclosed in copending patent applications of applicant's assignee including "Apparatus for Sealing a Hem in a Moving Web of Film Using Angularly Oriented Hot Wheels", Catchman and Herrington Ser. No. 904,449 filed Sept. 8, 1986, now U.S. Pat. No. 4,717,373; Apparatus for Sealing a Hem in a Moving Web of Film, Herrington, Ser. No. 904,441 filed Sept. 8, 1986, now U.S. Pat. No. 4,721,502 and Apparatus for Producing a Machine-Direction Heat Seal, Herrington, Ser. No. 904,444 filed Sept. 8, 1986, now U.S. Pat. No. 4,721,501. The foregoing applications are incorporated herein by reference thereto.
In forming hems in a moving web of film in the manufacture of plastic bags as disclosed in the above-identified patent applications the web of film is pulled over folding boards and a tucker bar is used to tuck an edge of the moving web onto the other side of each folding board so as to produce a hem. It has been found that variations in film gauge or tension sometimes cause the hem film to be loosely drawn around the edge of the board so that the hem is not well defined and bag length and hem width are not precise.
It is an object of the present invention to fold a hem in a moving web of film and to pull the film diagonally so that it is tight against the edge of the folding board prior to heat sealing the hem.
It is another object of the present invention to form hems in the opposing panels of the moving web of folded thermoplastic film in the manufacture of draw tape bags by utilizing tucker bars, that tuck the hem for the draw tape bags, equipped with a series of rubber wheels that pull the film diagonally so that it is tight against the edge of the folding board.